Phytoplankton Production and the Distribution of Nutrients in a Shallow Unstratified Estuarine System near Beaufort, N. C.

Abstract

Photosynthesis, nutrients, and phytoplankton standing crop were measured for one year at 32 stations in a system of shallow estuaries near Beaufort, N.C. Photosynthesis and chlorophyll had pronounced and similar seasonal distributions which roughly followed the cycle in water temperature. Production was generally minimal during December and maximal during June and July. Annual production at individual stations ranged from 16 g C/m² to 153 g C/m², and averaged 66.6 g C/m² for the 400 km² system. Phosphate concentrations were generally low throughout the year, ranging from of 0.00–1.46 μgA/liter. Nitrate values ranged from 0.00–2.65 μgA/liter, and ammonia from 0.00–4.30 μgA/liter. Maximum available nitrogen and phosphate concentration slightly preceded the period of maximum photosynthesis. Nitrogen and phosphorus were both probably limiting to phytoplankton in this system, but N:P ratios suggest that nitrogen was the more limiting.